The routing of transmissions through optical networks of the prior art is in many cases performed actively, using thermo-optical or optomechanical switches, or using devices that require conversion from the optical to the electrical domain and back. Such active devices tend to add significant expense to the network infrastructure, and generally dissipate significant amounts of power.
One alternative approach to network architecture that avoids the above disadvantages is Time-Domain Wavelength-Interleaved Network (TWIN). TWIN is transparent, in the sense that each transmitted signal remains in the optical domain, at the same wavelength, all the way from the source node to the destination node. A unique wavelength (or set of wavelengths) is assigned to each destination node. Each source node is served by a multiwavelength source. Outgoing transmissions are packaged in the form of optical bursts, each in a specified wavelength channel. In traversing the network, each signal passes through one or more wavelength-selective cross-connects, which ultimately steer each burst to its intended destination. Thus, the wavelength channel assigned to an outgoing burst is, in effect, an intrinsic destination label for that burst.
In the absence of coordination among the source nodes, it is possible for bursts to collide at the destination. That is, bursts from two disparate sources might wholly or partially coincide when received at the destination node. The resulting interference will often be irresolvable. It is also possible in some cases for a single source to be scheduled to send out bursts to two disparate destinations in the same timeslot. Although an occurrence of this kind is also in some sense a “collision,” we have here chosen to refer to it as a “source conflict.” One solution to the problem of collisions, as well as of source conflicts, has been described in U.S. patent application Ser. No. 10/426,389 which was filed by K. Kumaran et al. on Apr. 30, 2003 and is commonly assigned herewith. The solution described there involves a centralized scheduler which coordinates the source nodes, while also taking into account the respective transmission delays between each source-destination pair.
Although coordinated scheduling provides a useful solution to the problem of collisions, there are also potential advantages to alternative solutions, particularly when traffic is asynchronous, i.e., characterized by dynamically varying bandwidth demands.